The present invention relates to an electronic circuit for controlling nonlinear paths.
The object of a regulator is to bring a physical variable, the controlled variable X, to a predetermined nominal value, the reference variable W, and to keep it there. To this end, the regulator needs to counteract the influence of disturbances, in some suitable way.
Normally, a simple control loop has a regulator which influences the controlled variable X by means of a manipulated variable Y, such that the control error Wxe2x88x92X is as small as possible.
If the controlled variable is represented by an electrical voltage and the path is electrically controlled, electronic regulators can be used.
In its simplest form, such a regulator is an amplifier which amplifies the control error Wxe2x88x92X. If the controlled variable X rises above the nominal value W, then Wxe2x88x92X becomes negative. The manipulated variable Y is thus reduced to an increased extent. This reduction counteracts the assumed increase in the controlled variable, thus producing negative feedback. As the gain of the regulator becomes higher, the remaining control error in the steady state becomes lower.
In order to improve the adjustment accuracy of a proportional (P) regulator and in order to achieve a remaining control error of zero, an integrator is connected in parallel with a P regulator. A simple PI (proportional plus integral) regulator such as this behaves like an integrator at low frequencies, and like a pure proportional amplifier at high frequencies.
In practice, control paths often have a nonlinear response. For example, transistor amplifiers or diode rectifiers have nonlinear characteristic curves. The transfer function characteristics often have saturation effects at the control limits. The transfer function characteristics are also influenced by the operating voltage, input level and temperature.
For small disturbances about a given operating point, any path can be regarded as being linear, provided its characteristic curve in the vicinity of this operating point is continuous and can be differentiated. The regulator can now be optimized for this fixed operating point. However, if major changes in the reference variable W will be permissible, problems occur. Since the differential path gain is dependent on the operating point, the steady-state response of the configuration varies as a function of the reference variable W. The stability and control accuracy of the regulator also become poorer. The accuracy of a regulator is influenced by the accuracy of the controlled variable detector, the gain and the regulator offset.
This problem can be overcome in a known manner by linearizing the path by a function network connected upstream. If this linearization block has the inverse characteristic curve to that of the path to be linearized, then this results in a linear path equation overall. If, for example, the path has an exponential response, a logarithm former is required as the function network or linearization block. Such linearization is known, for example, from Tietze, Schenk: Halbleiter-Schaltungstechnik [Semiconductor circuit technology], 10th Edition, 1993, pages 951 to 952.
The additional linearization block is normally subject to drift with temperature or age. Furthermore, the control system overall becomes slower, since the additional linearization block has delay-time effects, of course. Since the known linearization block is configured at the output of the regulator and upstream of the control path, considerable currents flow there. Furthermore, a considerable voltage change can be expected at the output of a control amplifier which, for example, may be an operational amplifier in a simple embodiment. The design of a circuit configuration for an implementation block is thus subject to stringent requirements. In particular, a considerable chip surface area is required.
It is accordingly an object of the invention to provide a circuit configuration for controlling nonlinear paths which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type, and which can be produced at low cost.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for controlling nonlinear paths that includes a regulator having an output for providing a manipulated variable and having a plurality of inputs which include a first input and a second input. A nonlinear control path has an input connected to the output of the regulator and has an output for providing a controlled variable. A feedback path has a first linearization block disposed therein. The first linearization block has an input connected to the output of the control path and has an output connected to one of the plurality of the inputs of the regulator. A second linearization block has an output connected to one of the plurality of the inputs of the regulator. The second linearization block has an input for receiving a reference variable.
The circuit configuration for controlling nonlinear paths is based on the principle of arranging linearization blocks at the regulator input rather than at the regulator output. Since considerably lower currents can be expected at a regulator input than at the output, and the voltage change that occurs is considerably smaller, the linearization blocks, can be designed to be simpler. Furthermore, if the electrical power levels which can be expected are relatively low, considerably smaller chip surface areas are required. In addition, the signal processing for relatively low power levels is simpler.
Linearization blocks which are nonlinear blocks are normally subject to temperature drift and tolerances which can be governed, for example, by manufacturing or environmental conditions. Since two linearization blocks are connected to the regulator input or inputs in the described configuration, with one linearization block being configured in a feedback path and a second linearization block being configured at the nominal-value or reference-value supply, their temperature drift and tolerances cancel one another out.
In accordance with an added feature of the invention, the first and second linearization blocks are identical.
In accordance with an additional feature of the invention, the first and the second linearization blocks each have a function which is the inverse of that of the control path. The characteristic curves of the first linearization block and of the second linearization block are, in consequence, each an inverse of the characteristic curve of the path. The characteristic curve of the path may in this case be composed of the characteristic curves of a number of blocks in the path, for example amplifier stages.
In accordance with another feature of the invention, the regulator is a PI regulator. Regulators with an I element have a very high steady-state accuracy.
In accordance with a further feature of the invention, the regulator is in the form of a simple operational amplifier. Thus, if a regulator is intended to have an I element, a capacitor is connected between the output of the operational amplifier and the inverting input of the operational amplifier.
In accordance with a further added feature of the invention, if the described control system is used in a transmission amplifier for the field of mobile radio devices, the control path may have two series-connected transistor amplifier stages. Transistor amplifiers normally have nonlinear characteristic curves.
In accordance with a further additional feature of the invention, in order to detect the controlled variable, a detector can be configured in the feedback path between the output of the path and the first linearization block.
In accordance with yet an added feature of the invention, in order to compensate for temperature drift or tolerances in this detector, a further detector having the same electrical properties can be connected upstream of the second linearization block. In this case, the reference variable can be supplied to the further detector.
In accordance with yet an additional feature of the invention, in order to produce a differential amplifier, the first linearization block, which is configured in the feedback of the control loop, can be connected to a first input of the regulator, and a second linearization block can be connected to a second input of the regulator. If an operational amplifier is used as the control amplifier, the first linearization block can be connected to the inverting input of the operational amplifier, and the second linearization block can be connected to the noninverting input of the operational amplifier. Without negative feedback, a control system is not stable.
In accordance with a concomitant feature of the invention, the operational amplifier may be connected as an adder. In this case, the first and second linearization blocks are jointly connected to one input of the control amplifier. In this configuration, a resistor can in each case be configured between the output of the linearization block and the input of the operational amplifier.
Further embodiments of the present invention are specified in the dependent claims.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for controlling nonlinear paths, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.